1. Field of the Invention
The present invention relates to a mobile packet communication system and a method of mobile packet communication, and more particularly, to a mobile packet communication system and a method of mobile packet communication which are capable of transmitting a packet data to a specific base station area only in which a mobile station for a packet communication exists without broadcasting the packet data to all base station areas in a same location area.
2. Description of Related Art
A configuration of radio channels used in a mobile communication system is shown in FIG. 1. Radio channels are divided into two major categories, i.e. a traffic channel (TCH) which carries user traffic and a control channel (CCH) which is used to establish the TCH. The CCH is also divided into a broadcast control channel (BCCH), a common control channel (CCCH), a user packet channel (UPCH) and an associated control channel (ACCH). The BCCH, the CCCH and the UPCH are called the common access channels, as those channels are used by all mobile stations commonly, and the ACCH is called the user specific channel, as the ACCH is assigned to each TCH, i.e. the ACCH is associated with the TCH which is used by one mobile station for its call.
When a call is requested by a mobile station, a call request signal is transmitted to a mobile switching center through a base station by the CCCH, and a communication channel (TCH) allocated for the call is allocated to the mobile station from the mobile switching center by the CCCH. The CCCH is also used for broadcasting a paging signal to mobile stations when there is an incoming call to be received by a paged mobile station. The mobile station uses the allocated TCH for its communication to the other party. A channel switching signal or other signalling information necessary for controlling the call during communication is transmitted by the ACCH which is associated with the TCH. The BCCH is used for broadcasting a location code signal for location registration, number of control channels for allocating a control channel configuration. When communication information is transmitted by a packet form, the UPCH provided as the common channel is used, and the mobile communication system transmitting and receiving packet data signals by using the UPCH is called a mobile packet communication system.
An up-stream channel (signal direction from the mobile station to the base station: hereafter referred to as up-link) of the UPCH is used by a plurality of mobile stations on a random access basis and a down-stream channel (signal direction from the base station to the mobile station: hereafter referred to as down-link) of the UPCH is used as a basis for broadcasting. That is, a packet data signal on the down-link of the UPCH to a mobile station is broadcasted in all base stations in a location area, even if the mobile station to receive the packet data signal exists in one of base station areas.
The relation among the service area, the location area and the base station area of the mobile communication system will now be described.
The service area of a mobile communication system for mobile communication services consists of one or more location areas, each of which is identified by location information. A mobile station which is moving in the service area of the mobile communication can identify the location area, in which the mobile station exists at present, by receiving a location code signal broadcasted in each location area. When the mobile station has entered into a different location area, the mobile station recognizes the change of location area by receiving a different location code signal, and as the result, it requests a location registration to a location register through a nearest base station and a mobile switching center to update the location information of the mobile station stored in the location register.
The location information of the mobile station stored in the location register is retrieved and referred by the mobile switching center when the mobile switching center establishes a communication link to the mobile station for an incoming call. As the location area usually consists of a plurality of base station areas each of which is covered by the radio signal of a base station, the paging signal to page the mobile station for the incoming call is broadcasted from all base stations in the location area which has been identified by the location information in the location register.
FIG. 2 is a block diagram illustrating a conventional mobile packet communication system, and shows how a packet data is transmitted from a packet terminal (not shown in the drawing) in a fixed communication network 40 to the mobile station 11.
The location area 50 consists of a base station area A which is covered by radio signals of the base station 10 and a base station area B which is covered by radio signals of the base station 20. The base stations 10 and 20 are connected to the mobile switching center 30, and the mobile switching center 30 is connected to the fixed communication network 40. The mobile station 11 exists in the base station area A and the mobile station 21 exists in the base station area B. Signals from a call from the mobile station 11 are received by the base station 10 and are transferred to the mobile switching center 30 to establish a communication link either to the fixed network 40 or to the base station 20 depending on a routing information sent from the mobile station 11. In the case of incoming call, a call sent from the fixed network is received by the mobile switching center 30, and the mobile switching center 30 retrieves location information corresponding to the mobile station 11 to be called from the location register (not shown). Once the location area 50 in which the mobile station 11 to be called exists has been identified, the mobile switching center 30 instructs to broadcast paging signal to all base stations 10 and 20 in the location area 50.
If the call is a circuit call, such as voice communication other than the packet call, the communication link (the TCH) from a calling party to a called party (the mobile station 11) is established after the mobile station 11 has answered the paging signal, and after this, the signal for communication to the mobile station 11 are transmitted only from the base station 10 in the location area 50.
However, in the case of packet call, each packet data signal of packet communication is broadcasted from all base stations 10 and 20 in the same location area 50 even after the communication has commenced. This is because the communication link of the TCH dedicated to the call is not established for packet call, and only the UPCH provided for all mobile stations commonly is used. Therefore, the packet call 41 from the fixed network 40 is broadcasted as packet data signals 42 and 43 by the down-link of the UPCH in each of base station areas A and B although the packet data signal 43 is not used in the base station area B.
As described above, the conventional mobile packet communication system broadcasts each packet data signal of the packet communication in all base station areas in the same location area although the packet data signal is required by the mobile station existing in one base station area. This causes problems, in that:
(1) the transmission line and other relating equipment between the mobile switching center and each base station should be provided on the basis of unnecessary signalling capacity in addition to ordinary signalling capacity; and
(2) the data through-put of the UPCH is degraded when packet communications are performed in several different base station areas in the same location area because the down-link of the UPCH should carry all packet data signals to each base station area.